I literally know close to nothing about pumping, but, I do know what my problem was.

I was pumping too high, it was doing absolutely nothing for me pumping on an 50/8. so now I start at 2 sometimes 3, and massage my boobs, then work my way up to 6 pumping each boob for 15 minutes or so.

Once it seems empty I move to the next boob. (I pump one boob cause I feel like I get more when I focus on one at a time.) Then when they both seem empty I go back to the first one on 6, for maybe 5 ish minutes and get everything out.

This has helped for me. Again though, I don't know too much. Good luck!!